Researchers probe secrets of bacterial immune system

Scientists from New Zealand's University of Otago and the Netherlands are continuing to unlock the secrets of a surprisingly flexible bacterial immune system, called CRISPR-Cas.

Just like humans, bacteria are constantly under attack by viruses that try to infect them by injecting viral DNA. This foreign DNA (together with other invading DNA, such as plasmids) has a major impact on the evolution of microorganisms. For example, the spread of antibiotic resistance and virulence factors are often introduced via invasion by foreign DNA.

CRISPR-Cas systems can remember and destroy invading DNA by storing short, invader-derived, pieces of DNA (called 'spacers') into their genetic memory banks. In an earlier study, the team discovered that viruses and plasmids, which can avoid recognition by mutating their DNA, will trigger the bacteria's CRISPR-Cas system to respond by quickly acquiring new immunological memories from these mutated threats. This process is called 'primed adaptation'.

In their latest study, which appears this week in the prestigious journal Nature Communications, Associate Professor Peter Fineran's team sought to understand how these new memories were selected during the primed adaptation response.

Associate Professor Fineran explains; "We infected the bacteria with plasmids not previously encountered, or with mutated plasmids triggering the primed adaptation response. By making use of the advances in next generation sequencing through New Zealand Genomics Ltd, we analysed more than 20 million newly acquired spacers."

The team discovered that the acquisition of memories from plasmids not previously encountered was very inefficient in comparison to the mutated plasmids. By studying the order in which these new memories were acquired, the researchers developed a new model for primed adaptation.

"Examination of this order revealed that the origin of the first new memory had a remarkably strong influence on the origins of subsequent spacer selection," Dr Simon Jackson, a co-author on the study, says.

The data indicated that acquisition of new immunological memory occurs not only during primed adaptation but also as a consequence of direct defence against invading genetic elements that have not mutated to evade recognition by the CRISPR-Cas system.

"We propose that during CRISPR-Cas mediated defence, new immunity is generated as part of a positive feedback loop. This further reduces the risk of plasmids or viruses evading the bacteria's CRISPR-Cas defences through genetic mutations," says Dr Raymond Staals, the first author on the study.

Related Stories

New insights into a surprisingly flexible immune system present in bacteria for combating viruses and other foreign DNA invaders have been revealed by researchers from New Zealand's University of Otago and the Netherlands.

Like humans, bacteria come under attack from viruses and rely on an immune system to defend themselves. A bacterial immune system known as CRISPR helps microbes "remember" the viruses they encounter and more easily fend them ...

Bacteria's memories of hostile viruses are stronger than thought. Even when the intruders change their DNA sequence, the immune system of bacteria can recognise these and subsequently destroy them. That is the conclusion ...

A powerful genome editing tool may soon become even more powerful. Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab) have unlocked the key to how bacteria are able to "steal" genetic information from ...

The CRISPR/Cas9 protein system, which is central part to bacterial adaptive immunity, has soared to great prominence in recent years for its enormous potential as a genome editing tool. In studying this system, scientists ...

Bacteria may not have brains, but they do have memories, at least when it comes to viruses that attack them. Many bacteria have a molecular immune system which allows these microbes to capture and retain pieces of viral DNA ...

Recommended for you

Using a new type of dual polymer material capable of responding dynamically to its environment, Brown University researchers have developed a set of modular hydrogel components that could be useful in a variety of "soft robotic" ...

When more women are involved in group decisions about land management, the group conserves more—particularly when offered financial incentives to do so, according to a new University of Colorado Boulder study published ...

A new study by UAlberta biologists shows the first evidence of apoptosis, or programmed cell death in algae. The outcomes have broad-reaching implications, from the development of targeted antibiotics to the production of ...

New photonic tools for medical imaging can be used to understand the nonlinear behavior of laser light in human blood for theranostic applications. When light enters biological fluids it is quickly scattered, however, some ...

One of the ocean's little known carnivores has been allocated a new place in the evolutionary tree of life after scientists discovered its unmistakable resemblance with other sea-floor dwelling creatures.

In research that casts cells as curators of their own history, Dana-Farber Cancer Institute scientists have discovered that adult tissues retain a memory, inscribed on their DNA, of the embryonic cells from which they arose. ...

0 comments

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.